Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$78.56	7.715%	$84.6209	$84.62	$84.60	$84.60
Purchase #2	$213.45	10.851%	$236.6115	$236.61	$236.60	$236.60
Purchase #3	$100.56	6.150%	$106.7444	$106.74	$106.75	$106.70
Purchase #4	$53.96	9.638%	$59.1607	$59.16	$59.15	$59.20
Purchase #5	$100.27	13.142%	$113.4475	$113.45	$113.45	$113.40
Purchase #6	$184.60	3.704%	$191.4376	$191.44	$191.45	$191.40
Purchase #7	$78.50	7.589%	$84.4574	$84.46	$84.45	$84.50
7 purchase totals =	$809.90		$876.4800	$876.48	$876.45	$876.40